The present invention relates to a method and apparatus for conditioning tobacco. More particularly, the invention relates to improvements in a method and apparatus for drying particles of tobacco which are transported in the form of a continuous stream.
Tobacco driers are becoming increasingly important components of primary tobacco processing equipment. This is due to the fact that the manufacturers of cigarettes or other smokers' products demand an extremely accurate conditioning of tobacco prior to admission into a cigarette maker or a like machine. The final moisture content of conditioned tobacco particles must match a preselected optimum value, and each and every portion of each tobacco particle must or should be dried to the same extent. Such high degree of homogeneousness (as regards the final moisture content of conditioned tobacco) cannot be achieved in accordance with heretofore known methods and by resorting to heretofore known primary tobacco processing equipment. One of the reasons for inability of conventional primary processing equipment to meet the aforediscussed stringent requirements regarding the final moisture content of each and every portion of each particle of conditioned tobacco is that the conditioning invariably involves treatment of large quantities of tobacco particles per unit of time. The initial moisture content of tobacco which is admitted into the first unit of a primary processing equipment invariably fluctuates above and below an anticipated (predetermined) value. Therefore, the drying action upon successive increments of a tobacco stream which is conveyed through the conditioning zone or zones must fluctuate in order to achieve a more pronounced drying action when the initial moisture content is relatively high and to reduce the intensity of drying action when the initial moisture content of tobacco particles entering the first stage of primary processing equipment is relatively low.
Heretofore known attempts to insure that the final moisture content of conditioned tobacco particles will match a preselected optimum value include the provision of highly complex, expensive and sensitive control systems which detect fluctuations of the initial moisture content and regulate the drying action in dependency on deviations of initial moisture content from an anticipated (predetermined) value. It was also proposed to subject tobacco particles which leave the drying unit to a secondary conditioning action, for example, in a manner as disclosed in commonly owned U.S. Pat. No. 4,143,471 granted Mar. 13, 1979. Such secondary conditioning normally insures that the moisture content of tobacco particles which leave the secondary conditioning equipment matches or closely approximates a preselected value. However, secondary conditioning is less effective if the condition of tobacco particles which enter the primary conditioning zone is not uniform; under such circumstances, the drying action is likely to be less satisfactory than in the absence of secondary conditioning equipment.